Bring 4 cups water to a boil in a 3- to 3 1/2-qt. saucepan over medium-high heat.
Add oranges. Return to a boil; cook 5 minutes.
Transfer oranges to a parchment paper-lined jelly-roll pan, using a slotted spoon; discard water.
Combine sugar and 2 cups water in saucepan. Scrape seeds from vanilla bean into water; add vanilla bean to water. Bring to a boil over medium-high heat, stirring occasionally, until sugar is dissolved.
Add orange slices. Return to a boil; cover, reduce heat to medium, and simmer 10 minutes. Uncover and cook, stirring occasionally, 35 to 45 minutes or until rinds are softened and translucent.
Remove oranges, using tongs; arrange on parchment paper-lined jelly-roll pan, folding oranges as desired. Blot with paper towels.
Pour syrup through a fine wire-mesh strainer into a bowl, reserving syrup and vanilla bean for another use. Discard solids.
